1. Field of the Invention
The invention relates to a flowable concrete mixture of cement glue and aggregates for the production of steel concrete or prestressed concrete.
2. Description of the Prior Art
Concrete is a mixture of cement glue, i.e., a mixture of cement and water and solid components, the latter being the so-called aggregates. These aggregates consist of natural or artificial, dense or porous rock and have particle sizes which are suited for the purpose of the concrete. In accordance with current concrete technology, the aggregates which are graded according to certain particle sizes, form a so-called granular skeleton in which the individual particles contact and support each other. Between the particles or aggregates are spaces or voids. The cement glue fills these hollow spaces and bonds the particles together. Accordingly, a certain ratio by volume of aggregates and cement glue must be present, i.e., the amount of cement glue is that volume necessary to fill the hollow spaces. An excess of one or the other, for example, cement glue, would lead to immediate segregation since the particles of the aggregates support one another and would sink to the bottom. The cement glue thus settles at the surface and this leads to the formation of cracks.
When placing the fresh concrete in the formwork, the concrete must be compacted by using vibrating devices to achieve a dense structure and a complete covering of the steel reinforcements as well as to avoid structural pores in the concrete structure and in the end surfaces at the formwork. These structural pores are caused by enclosed air bubbles. These requirements must be followed the more exact, the denser the structural element to be produced is reinforced.
The energy required for a correct compacting of the concrete depends on the consistency of the concrete. This consistency, in turn, depends largely on the cement glue content of the concrete as well as on the particle size and the volume weight of the aggregates. The lower the cement glue content, the dryer the content and the larger the energy requirement for compacting, for example, by tamping or vibrating. The larger the cement glue content, the softer the concrete and the better the workability of the concrete. The strength of the concrete is largely determined by the quality of the cement glue and by the ratio by weight of the water and the cement contained in the concrete, the so-called water-cement ratio. The addition of water alone improves the workability of the mixture, however, the strength properties are changed.
It is known to improve the flow properties of concrete by adding chemical admixtures. These admixtures counteract the inner friction of the mixture. However, these admixtures are effective only over a limited time. They cause the heavier components of the aggregates to settle out more than the lighter components because the inner friction is eliminated, especially, when the consistency of the fresh concrete is soft. This is disadvantageous in that, in the finished concrete, a layering of the aggregates may occur corresponding to the volume weight of the individual components.